The Privileged Pincer-Metal Platform: Coordination Chemistry & Applications

Table of Contents

1. Frontmatter

2. Modern Organometallic Multidentate Ligand Design Strategies: The Birth of the Privileged “Pincer” Ligand Platform

   Preston A. Chase, Robert A. Gossage, Gerard van Koten

   Abstract

   The seemingly simple tridentate ligand design, one that is now known as the “pincer,” has gained increasing importance in metal–ligand chemistry and in other applications as diverse as organic synthesis, catalysis, and materials science. This chapter describes the historical context in which the pincer ligand platform developed and sketches how Shaw’s research played a crucial early role. The original chemistry, emerging in the late 1970s and early 1980s, is presented which details the synthesis and properties of the first examples of pincer-based organometallic complexes along with a selection of related species. Finally, a connection is made from this early start to the excellent and striving studies that currently are ongoing in pincer chemistry and its applications thereof.

3. Pincer Complexes of Lithium, Sodium, Magnesium and Related Metals: A Discussion of Solution and Solid-State Aggregated Structure and Reactivity

   Robert A. Gossage

   Abstract

   An overview of the Li, Na, Mg and Cu complexes of the pincer ligands is presented. This discussion will include common techniques and advances in the synthesis of the title materials, their properties (notably in the solid state) and trends in their reactivity. In addition, a brief description of the known “mixed” or hetero-aggregated pincer complexes will also be given.

4. Late Transition Metal Complexes with Pincer Ligands that Comprise N-Heterocyclic Carbene Donor Sites

   Kevin Farrell, Martin Albrecht

   Abstract

   The incorporation of N-heterocyclic carbenes into the well-established pincer ligand platform entails a number of attractive benefits. For example, NHCs are strong donors, and the metal–carbene bond is often remarkably robust towards oxidative and hydrolytic conditions and thus sustains in air, moisture, and even highly acidic environments. Moreover, NHCs can be readily functionalized and modulated and thus provide excellent opportunities for fine-tuning the properties of a coordinated metal center. As a consequence, the combination of the concepts of pincer ligands and of NHCs has much appeal and continues to attract considerable interest. This chapter summarizes accomplishments over the last 5 years in the domain of pincer carbene complexes containing Group 8–10 metals, including synthetic aspects as well as application of these complexes, which has included in particular catalysis and to a lesser extent materials science and medicinal areas.

5. Rare Earth Pincer Complexes: Synthesis, Reaction Chemistry, and Catalysis

   Mikko M. Hänninen, Matthew T. Zamora, Paul G. Hayes

   Abstract

   The research field surrounding rare earth pincer complexes has reached a stage where a comprehensive review about the reactivity and catalytic behavior of these species is justified. In this contribution, we begin with a brief introduction on common strategies for the preparation of rare earth pincer complexes, continuing with a section devoted to the versatile reactivity observed for this class of compound. Thereafter, several types of compounds are discussed, including extremely reactive hydrides, cationic species, and intriguing scandium imido complexes. Finally, the last portion of this chapter sums up the hitherto reported catalytic studies, including discussions on ring-opening polymerization of cyclic esters, polymerization of olefins and hydroamination reactions, as well as several examples of more infrequently encountered catalytic processes.

6. New Chemistry with Anionic NNN Pincer Ligands

   Rebecca L. Melen, Lutz H. Gade

   Abstract

   The use of tridentate anionic pincer ligands in organometallic chemistry has gained considerable importance, particularly in the field of homogenous catalysis. This chapter focuses on the recent developments of anionic tridentate NNN pincer ligands from their synthesis to coordination chemistry and their applications in forming stable transition metal complexes for applications in catalytic transformations.

7. Pincer Complexes with Thione Sulfur Donors

   Diana V. Aleksanyan, Vladimir A. Kozlov

   Abstract

   Rapid development of pincer chemistry over the last several decades made a substantial contribution in extension of theoretical and practical organometallic chemistry as well as organic synthesis, catalysis, and materials science. This review is devoted to relatively new types of nonclassical pincer compounds bearing thione sulfur donors incorporated into thiophosphoryl and/or thioamide groups. The discussion is focused on synthetic aspects and structural features of symmetrical and hybrid S,C,S-pincer ligands and complexes with particular attention to the practically valuable properties.

8. Recent Advances on the Chemistry of POCOP–Nickel Pincer Compounds

   Matthew Asay, David Morales-Morales

   Abstract

   A description of the vertiginous development of the chemistry of POCOP–Ni complexes and their applications is described. Recent advances include the discovery and initially challenging synthesis of these species to the high-yield green procedures recently developed. The various applications of these compounds, particularly in catalysis, are discussed in detail.

9. Pincerlike Cyclic Systems for Unraveling Fundamental Coinage Metal Redox Processes

   Marc Font, Xavi Ribas

   Abstract

   Pincerlike cyclic ligands have overcome the high instability of transition metals in their higher oxidation states and have permitted the isolation of such species and the exhaustive study of their properties and reactivity. The formation and isolation of organometallic Cu^II and M^III (M=Cu, Ag, Au) complexes stabilized by NCPs, carbaporphyrins, carbaporphyrinoids, heterocalixarenes, and triaza macrocyclic ligands will be discussed in this chapter. The study of these complexes have led to the discovery of unprecedented reactivity and proved the plausibility of often invoked pathways in copper-catalyzed cross-coupling reactions. Aryl-M^III (M=Cu, Ag) stable species have been implicated as the key intermediate species that operate in coupling catalysis through two-electron redox cycles involving oxidative addition and reductive elimination fundamental steps.

10. Recent Advances in Alkane Dehydrogenation Catalyzed by Pincer Complexes

    Akshai Kumar, Alan S. Goldman

    Abstract

    Olefins are ubiquitous intermediates in the production of fuels and commodity chemicals. Accordingly, the development of methods for the selective dehydrogenation of alkanes to give olefins is a goal with great potential value. Molecular (homogeneous) catalysts appear quite promising in this respect. Great advances have been seen with pincer-ligated catalysts since the mid-1990s, particularly (but not exclusively) with iridium complexes. In this chapter we give an overview of this productive area of research, with emphasis on recent progress.

11. Tethered Pincer Complexes as Recyclable Homogeneous Catalysts

    Aidan R. McDonald, Harm P. Dijkstra

    Abstract

    The utilisation of recyclable pincer complexes in applied catalysis is a vital progression in the field of homogeneous catalysis. This is routed in the high thermal and mechanical stability that most pincer complexes demonstrate. The pincer framework of a tridentate bis-chelating ligand system, with two dative appendages and a direct metal ligand σ-bond, shows higher stability than most other coordination complexes. This is essential to testing immobilisation and recycling methods for homogeneous catalysis. We review herein efforts made towards the efficient immobilisation (heterogenisation) of homogeneous pincer complexes, and their application in a variety of catalytic processes. Recycling of pincer complexes, as described herein, does not display high rates of ligand and metal leaching. The outcome of this is an array of homogeneous catalyst immobilisation techniques which can be probed using pincer complexes.

12. Backmatter